As generally known in the art, PCBs conventionally employ copper rated 0.5-2.0 oz, and the thickness of copper in this case is about 18-70 μm (the thickness of copper per 1 oz is about 35 μm). For example, in the case of a PCB requiring a high current, the sectional area of copper of inner layers is preferably increased. In order to increase the sectional area of copper, the thickness of copper of the PCB must have a large value, and heavy copper (at least 4 oz) is commonly used for PCBs.
In the case of heavy copper of about 4 oz, the thickness is about 140 μm. If multilayered wiring is to be constructed on a PCB having such thick copper, the space between copper, which has a resin pattern, may left unfilled in the lamination step.
Particularly, referring to FIG. 1, which shows a conventional process for manufacturing multilayered PCBs, a prepreg 20, which is obtained by impregnating a substrate with a resin, is compressed at high temperature and pressure in a lamination process so that the space between patterns is filled. If copper 11 of the core layer has a step as thick as 140 μm, voids 30a, 30b, 30c, 30d may be formed between copper patterns.
Various methods have been proposed to solve the above-mentioned problems.
For example, Korean Laid-open Patent Publication No. 2004-0111302 proposes a method of printing stepped portions of copper by using an epoxy material. However, this method is not suited to mass production, and increases the manufacturing cost.
Furthermore, Korean Laid-open Patent Publication No. 2005-0112365 proposes technology of using RCC (Resin Coated Copper), which contains no substrate, as a buildup material in order to increase the resin content ratio of the buildup material used in the lamination process. However, this technology has a problem in that, since the buildup material contains no substrate but only a resin, it is structurally and thermally unstable (i.e. vulnerable to mechanical and thermal impact), and is expensive.
Therefore it is requested to manufacture a PCB having multiples layers of heavy copper, which is inexpensive and thermally stable, and which makes it possible to simplify the processes without creating voids during lamination.